A nickel-hydrogen rechargeable battery with an anode containing a hydrogen storage alloy has a higher energy density than a nickel-cadmium rechargeable battery, and places only a small burden on the environment due to absence of toxic Cd. Nickel-hydrogen rechargeable batteries are used in portable devices such as digital cameras and electric tools as well as in electric vehicles and hybrid electric vehicles. Various battery characteristics are desired depending on applications.
As an anode material for a nickel-hydrogen rechargeable battery, hydrogen storage alloys have been developed and used, such as those of LaNi5 type containing AB5 crystals as the main phase, those having a Laves phase as the main phase, and those having a BCC (body-centered cubic lattice) phase as the main phase.
Rare earth-Mg—Ni based hydrogen storage alloys have recently been put into practical use. Nickel-hydrogen rechargeable batteries employing this alloy are known to have a large capacity.
Patent Publication 1 is directed to a method for producing a rare earth-Mg—Ni based hydrogen storage alloy by melting, and discloses to inhibit evaporation of Mg by regulating the temperature of the rare earth-Mg—Ni-alloy melt and the pressure in the melting furnace to predetermined values.
Patent Publication 2 discloses a method for producing an alloy containing one or more of Mg, Ca, Li, Zn, Mn, and Sr by melting in a helium-containing gas atmosphere. In Examples, methods for preparing alloys such as MgNi2 are disclosed.
Patent Publication 3 discloses a hydrogen storage alloy containing Mg and having a BCC lattice structure, and a method of producing the alloy by mechanical alloying.    Patent Publication 1: WO 2005/080617    Patent Publication 2: WO 2006/093334    Patent Publication 3: JP 2004-292838-A